To recap, users who add their debit card information in Messenger's settings section can send payments by starting a conversation with one or more friends, picking the "$" icon that appears in the row above the software keyboard, and tapping "Pay." Users who receive money do so by opening up that friend's message and accepting the payment when prompted. And just like bank deposits, payment may take up to three business days to go through.

Facebook users can only add their debit card information for now, a decision the company said was made to minimize fraud and avoid fees. (Existing peer-to-peer payments app Venmo lets users add credit cards, but there's a small catch: a 3% fee on each transaction.)

The Messenger team has taken its time with payments since the long-awaited feature was announced in March, gradually rolling it out across the country to a handful of cities first before going nationwide — a cautious approach likely done to avoid potential security issues. Along the way, the Messenger team also beefed up payments with features like the ability to pay inside group chats.

While Marcus has previously said the Messenger team has no plans of making Messenger a deep, multi-faceted platform to rival mature payments businesses like PayPal — the company he previously ran — the move into mobile payments makes a lot of sense given that space is poised to nearly triple in volume from $52 billion in 2014 to $142 billion in 2019, according to Forrester Research.

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